Synergistic welding system

ABSTRACT

A welding system is disclosed for performing a short arc welding process between an advancing wire electrode and a workpiece. The system comprises a power source with a controller for creating a current pulse introducing energy into the electrode to melt the end of the electrode and a low current quiescent metal transfer section following the end of the melting pulse during which the melted electrode short circuits against the workpiece; a timer to measure the actual time between the end of the pulse and the short circuit; a device for setting a desired time from the pulse to the short circuit; a circuit to create a corrective signal based upon the difference between the actual time and the desired time; and, a circuit responsive to the corrective signal to control a given parameter of the current pulse. Also disclosed is a strategy for arc welding utilizing a cored electrode that produces welds with low levels of contaminants and which are strong, tough, and durable. The arc welding process generally utilizes an AC waveform. The cored electrode can be a self-shielded flux cored electrode (FCAW-S). Various electrode compositions are described that are particularly beneficial when used in conjunction with an AC waveform.

The present invention relates to the art of electric arc welding andmore particularly to an improved short arc welding system, methods ofwelding with self-shielded flux cored arc welding (FCAW-S) electrodes,and the composition of the electrodes.

INCORPORATION BY REFERENCE

This invention involves a novel short arc welding process employing anovel cored electrode. There is a synergistic relationship whencombining the novel welding process and the novel flux cored electrode.As an attribute of the overall invention, there are independentadvantages of the novel process combined with the flux cored electrode.

Short Arc Welding

Short-circuit arc welding systems, techniques, and associated concepts,as well as pipe welding methods and apparatuses are generally set forthin the following United States patents, the contents of which are herebyincorporated by reference as background information: Parks U.S. Pat. No.4,717,807; Parks U.S. Pat. No. 4,954,691; Parker U.S. Pat. No.5,676,857; Stava U.S. Pat. No. 5,742,029; Stava U.S. Pat. No. 5,961,863;Parker U.S. Pat. No. 5,981,906; Nicholson U.S. Pat. No. 6,093,906; StavaU.S. Pat. No. 6,160,241; Stava U.S. Pat. No. 6,172,333; Nicholson U.S.Pat. No. 6,204,478; Stava U.S. Pat. No. 6,215,100; Houston U.S. Pat. No.6,472,634; and Stava U.S. Pat. No. 6,501,049.

Power Source

The electric arc welding field uses a variety of welding processesbetween the end of a consumable advancing electrode and a workpiece,which workpiece may include two or more components to be weldedtogether. This invention relates to the short arc process wherein theadvancing electrode is melted by the heat of the arc during a currentpulse and then, after the molten metal forms into a ball by surfacetension action, the molten metal ball is transferred to the workpiece bya short circuit action. The short circuit occurs when the advancing wiremoves the ball into contact with the molten metal puddle on theworkpiece, which short is sensed by a plunge in the welding voltage.Thereafter, the short circuit is broken and the short arc weldingprocess is repeated. The invention is an improvement in short arcwelding and is preferably performed by using a power source wherein theprofile of the welding waveform is controlled by a waveform generatoroperating a pulse width modulator of a high switching speed inverter, asdisclosed in several patents by assignee, such as shown in Parks U.S.Pat. No. 4,866,247; Blankenship U.S. Pat. No. 5,278,390; and, HoustonU.S. Pat. No. 6,472,634, each of which is hereby incorporated byreference. These three patents illustrate the type of high switchingspeed power source employed for practicing the preferred embodiment ofthe present invention and are incorporated herein as backgroundtechnology. The waveform of the waveform generator is stored in memoryas a state table, which table is selected and outputted to the waveformgenerator in accordance with standard technology pioneered by TheLincoln Electric Company of Cleveland, Ohio. Such selection of a tablefor creating the waveform profile in the waveform generator is disclosedin several prior art patents, such as the previously mentionedBlankenship U.S. Pat. No. 5,278,390. Consequently, a power source usedin practicing the present invention is now commonly known andconstitutes background technology used in the present invention. Anaspect of the novel short arc welding system of the present inventionemploys a circuit to determine the total energy of the melting pulseforming the molten metal ball of the advancing electrode, such asdescribed in Parks U.S. Pat. No. 4,866,247. The total energy of themelting pulse is sensed by a watt meter having an integrated output overthe time of the melting pulse. This technology is incorporated byreference herein since it is employed in one aspect of the presentinvention. After a short has been created in a short arc welding system,the short is cleared by a subsequent increase in the welding current.Such procedure is well known in short arc welding systems and isdescribed generally in Ihde U.S. Pat. No. 6,617,549 and in Parks U.S.Pat. No. 4,866,247. Consequently, the technology described in Ihde U.S.Pat. No. 6,617,549 is also incorporated herein as background technology.The preferred embodiment of the invention is a modification of astandard AC pulse welding system well known in the welding industry. Aprior pending application of assignee describes standard pulse welding,both DC and AC, with an energy measurement circuit or program for a highfrequency switching power source of the type used in practicing the ACshort circuit preferred implementation of the present invention.Although not necessary for understanding the present invention orpracticing the present invention, this prior application, which is Ser.No. 11/103,040 filed Apr. 11, 2005 (LEEE 200548), is incorporated byreference herein. Also incorporated herein by reference is U.S.application Ser. No. 10/959,587 filed Oct. 6, 2004 (LEEE 200441).

The present invention relates to a cored electrode and a short arcwelding system for controlling the melting pulse of the system fordepositing a special cored electrode so no shielding gas is needed. Thesystem maintains a desired time between the pulse and the actual shortcircuit. This time is controlled by a feedback loop involving a desiredtiming of the short circuit and the pulse, so that the size of the ballof the pulse is varied to maintain a consistent short circuit timing.This process is a substantial improvement of other short arc controlarrangements, such as disclosed in Pijls U.S. Pat. No. 4,020,320 usingtwo power sources. A first source maintains a constant size meltingpulse and there is a fixed time between the short circuit and thesubsequent clearing pulse. There is no feedback between the pulsedtiming and a parameter of the melting pulse, as employed in the presentinvention. A desired time is maintained between the end of the meltingpulse and the short circuit event. By fixing the desired time using afeedback loop concept, arc stability is improved. This invention isapplicable to a DC process, as shown in Pijls U.S. Pat. No. 4,020,320,but is primarily advantageous when using an AC short arc welding system.Consequently, Pijls U.S. Pat. No. 4,020,320 is incorporated by referenceherein as background technology showing a control circuit for a DC shortarc system wherein two unrelated timings are maintained constant withouta closed loop control of the melting pulse.

Cored Electrode

The invention involves a novel welding method employing a novel fluxcored electrode or welding wire. Details of arc welding electrodes orwires and specifically, cored electrodes for welding are provided inU.S. Pat. Nos. 5,369,244; 5,365,036; 5,233,160; 5,225,661; 5,132,514;5,120,931; 5,091,628; 5,055,655; 5,015,823; 5,003,155; 4,833,296;4,723,061; 4,717,536; 4,551,610; and 4,186,293; all of which are herebyincorporated by reference.

Also, prior applications filed Sep. 8, 2003 as Ser. No. 10/655,685 (LEEE200329); filed Apr. 29, 2004 as Ser. No. 10/834,141 (LEEE 200408); filedOct. 6, 2004 as Ser. No. 10/959,587 (LEEE 200441); and filed Oct. 31,2005 as Ser. No. 11/263,064 (LEEE 200663) are each incorporated byreference as background, non-prior art technology.

THE INVENTION

In accordance with a first aspect of the invention as it relates to themethod, the melting pulse of the short arc waveform is controlledinteractively by a feedback loop and not by fixing constant values ofthe melting pulse. The time between the end of the melting pulse and theshort circuit is maintained by reactively changing parameters of themelting pulse in a short arc welding system. The system is preferably anAC system, but can be used in a DC system of the type generallydescribed in Pijis U.S. Pat. No. 4,020,320. Novel manipulation of theshort arc waveform is facilitated by using a single power source havingthe waveform controlled by a waveform generator operating the pulsewidth modulator of a high switching speed inverter, such as disclosed inHouston U.S. Pat. No. 6,472,634. The advance realized by implementationof the present invention is an improvement over short arc welding usingtwo separate power sources, as shown in the prior art.

In accordance with the preferred embodiment of the first aspect of thepresent invention, the short arc welding system is an AC system whereinthe melting pulse has a negative polarity. To maintain a constant moltenmetal bead, there is a joule threshold switch to shift the power supplyto a low level positive current so the molten metal on the end of theadvancing electrode forms into a ball and then short circuits againstthe workpiece weld puddle. This AC waveform is preferably controlled bya waveform generator controlling the profile of the individual currentsegments of the waveform and determining the polarity of the waveformsegments. In the prior art, a joule threshold switch was used to providea constant energy to the melting pulse. In accordance with the presentinvention, there is a timer to measure the time for the electrode toshort after the melting pulse. A feedback loop is employed to maintain aconsistent time between the melting pulse and the short circuit event.This control of time stabilizes the arc and the shorting cycle. Ideallythe time between the melting pulse and the short is about 1.0 ms.Depending upon the electrode size and deposition rate, the time betweenthe melting pulse and the short circuit event is adjusted to a fixedvalue in the general range of 0.5 ms to 2.0 ms. Control of the timing isprimarily applicable to AC short arc welding; however, the same conceptis applicable to straight DC positive polarity. In both instances, theadvancing wire with molten metal formed by the melting pulse is held ata low quiescent positive current facilitating the formation of a ballpreparatory to the short circuit event. In either implementation of theinvention, the joules or other parameter of the melting pulse iscontrolled by a feedback loop conditioned to maintain a preset time tothe short circuit event.

The AC implementation of the first aspect of the present invention isprimarily useful for tubular electrodes of the flux cored type andespecially a novel implimentation of a flux core electrode with alloyingredients in the core. Control of the melting cycle of a flux coredelectrode based upon feedback from the short circuit time is a veryprecise procedure to maintain stability of the AC short circuit weldingprocess. The invention is also especially applicable to pipe weldingwith a cored electrode (especially the novel version of a flux coredelectrode). The welding current for such electrode, when using the novelmethod, is below the threshold current for spray welding. Thus, themetal transfer to the pipe joint must involve some type of shortcircuit, normally a globular short circuit transfer of the type to whichthe present invention is directed. Improving the weld stability by usingAC short arc welding still resulted in instability of the arc. Thisinstability has been overcome by implementing the present invention.Thus, the present invention is particularly applicable to AC short arcwelding of a pipe joint using a cored electrode.

In accordance with the first aspect of the present invention there isprovided a welding system for performing a short arc welding processbetween an advancing wire electrode and a workpiece, where the systemcomprises a power source with a controller for creating a current pulseintroducing energy into the electrode to melt the end of the electrodeand a low current quiescent metal transfer section allowing the meltedmetal on the end of the electrode to be deposited into the weld puddleof the workpiece. During the low current metal transfer section, themolten metal short circuits against the molten metal puddle. A timermeasures the actual time between the end of the melting pulse and theshort circuit event. A device is used to set a desired time between thepulse and short circuit event and a circuit is used to create acorrective signal based upon the difference between the actual time andthe desired time. This corrective signal is used to control a givenparameter of the melting pulse, such as the total energy introduced intothe wire during the melting pulse.

In accordance with the preferred implementation of the first aspect ofthe present invention, the short arc welding process is an AC processwherein the melting pulse is performed with a negative current and thequiescent low current metal transfer section of the waveform is at apositive polarity. The AC version of the present invention isparticularly applicable for welding with a flux cored electrode inseveral environments, such as the root pass of a pipe welding joint.

In accordance with another aspect of the novel power source, thecontroller of the short arc welding system includes a circuit to createa short circuit clearing pulse after the short circuit. In the preferredpower source a waveform generator determines the polarity and profile ofthe welding waveform at any given time. The welding system of thepresent invention is used to maintain the time between the melting pulseand the short at a fixed value, which fixed value is in the generalrange 0.5-2.0 ms and is preferably approximately 1.0 ms.

In accordance with another aspect of the power source or methodperformed by the power source, the short arc system is performed DCpositive with both the melting pulse and the quiescent section beingpositive and followed by a short circuit positive clearing pulse. Thisimplementation of the present invention does not involve a polaritychange from the waveform generator during the processing of the waveformto practice the short arc welding process. The short arc welding systemis AC and there is a circuit to control the current pulse for causingthe actual time between the melting pulse and short circuit so it is thesame as the desired time. Indeed, this implementation of the inventionmaintains a constant time, as does the preferred embodiment of theinvention.

The principal implementation of the present invention controls theenergy of the melting pulse to control the time between the meltingpulse and the ultimate short circuit event.

Yet another aspect of the first aspect of the invention is the provisionof a method for controlling the melting pulse of a short arc weldingprocess so that the process has a selected time between the meltingpulse and the short circuit event. The parameter controlled by thismethod is preferably the total energy of the melting pulse. Theinvention is particularly applicable for use in the root pass of acircular open root pipe joint using a flux cored electrode.

The present second aspect of the invention relates at least in part, toa discovery that by utilizing a relatively short arc length during ACwelding as obtained by this novel short arc method, contamination of theweld from the atmosphere can be significantly reduced. The inventionalso relates at least in part, to a discovery of a particular flux alloysystem, which when used in an electrode according to the second aspect.The flux/alloy system of the cored electrode enables and promotes ashort arc length. Combining these aspects in accordance with the presentinvention, provides a synergistic phenomenon, i.e. the novel method andnovel flux cored electrode that produces a sound and tough weld metalwith strength of over 60 to 70 ksi. These alloys allow use of thinnerpipes and there is no need for shielding gas in the pipe welding area.

Waveform technology as pioneered by The Lincoln Electric Company ofCleveland, Ohio has been modified for use in AC welding with flux coredelectrodes. Cored electrodes allow the welding operation to be moreprecisely controlled with the alloy of the weld bead being tailored tothe desired mechanical characteristics for the bead and with theposition of the welding operation being less limited. However, toprovide arc stability and appropriate melting temperatures and rates,the actual control of the waveform for the AC process is quitecomplicated. Contamination of the weld metal during arc welding is stilla problem using AC welding for cored electrodes. Contaminants, in theweld metal after the welding operation can cause porosity, cracking andother types of defects in the weld metal. Consequently, a majorchallenge confronting designers of arc welding processes has been todevelop techniques for excluding elements, such as contaminants from theatmosphere, from the arc environment or for neutralizing the potentiallyharmful effects of such impurities. The potential source ofcontamination, includes the materials that comprise the weldingelectrode, impurities in the workpiece itself and ambient atmosphere.Cored electrodes may contain “killing” agents, such as aluminum,magnesium, zirconium and titanium which agents combine chemically withpotential contaminates to prevent them from forming porosity and harmfulinclusion in the weld metal. The present invention involves the use of aunique, novel electrode composition that reduces the tendency of a coredelectrode to allow inclusion of contaminants in the weld metal. Themethod also reduces the amount of material required as a “killing”agent.

Specifically, the present invention provides a self-shielded flux coredarc welding (FCAW-S) electrode particularly adapted for forming weldshaving reduced levels of contaminants using an AC waveform. Theelectrode has an alloy/flux system comprising from about 35 to about 55%barium fluoride, from about 2 to about 12% lithium fluoride, from about0 to about 15% lithium oxide, from about 0 to about 15% barium oxide,from about 5 to about 20% iron oxide, and up to about 25% of adeoxidation and denitriding agent. This agent can be selected fromaluminum, magnesium, titanium, zirconium, and combinations thereof.

The present invention provides a method of arc welding using a fluxcored electrode that utilizes a particular alloy/flux system. The methodcomprises applying a first negative voltage between an electrode and asubstrate to cause at least partial melting of the electrode proximatethe substrate. The method also comprises applying a positive voltagebetween the electrode and the substrate to promote formation of aflowable mass of material from the electrode. The method furthercomprises monitoring for occurrence of an electrical short between theelectrode and the substrate through the flowable mass. The methodfurther comprises upon detecting an electrical short, applying a secondnegative voltage between the electrode and the substrate. And, themethod comprises increasing the magnitude of the second negativevoltage, to thereby clear the electrical short and form a weld on thesubstrate from the flowable mass. The flux cored electrode can comprisefrom about 35 to about 55% barium fluoride, from about 2 to about 12%lithium fluoride, from about 2 to about 15% lithium oxide, from about 5to about 20% iron oxide, and up to about 25% of a deoxidation anddenitriding agent selected from the group consisting of aluminum,magnesium, titanium, zirconium, and combinations thereof.

An object of the present invention is the provision of a short arcwelding system, which system controls the spacing of the short circuitevents during the process, especially when the process is performed inthe AC mode.

Another object of the present invention is the provision of a method forshort arc welding, which method controls the melting pulse based uponthe time between the melting pulse and short so this time remains fixedat a desired value.

Yet another object of the present invention is the provision of animproved electrode composition, and particularly an electrode fillcomposition which is particularly adapted for use in combination withthe novel short arc welding system and method.

A further object of the present invention is to provide a synergisticsystem comprising a short arc process and flux cored electrode tostabilize the arc at the shortest possible arc length. Thus, thecontamination from the atmosphere is minimized. The combination of analloy system and a weld process allows the arc to be stable at suchshort arc lengths and result in a sound and tough weld metal.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a short arc welding system used in thepreferred embodiment of the present invention;

FIG. 1A is an enlarged cross-sectional view taken generally along line1A-1A of FIG. 1;

FIG. 2 is a series of side elevational views showing the stages I-IV ina short arc welding process;

FIG. 3 is a combined current and voltage waveform graph showing thewaveform implementing the preferred embodiment of the present inventionas disclosed in FIG. 4 for the various stages as shown in FIG. 2;

FIG. 4 is a flow chart block diagram illustrating a modification of thesystem in FIG. 1 to perform the preferred embodiment of the presentinvention;

FIGS. 5 and 6 are flow chart block diagrams of a portion of the weldingsystem shown in FIG. 1 for implementing two further embodiments of thepresent invention;

FIGS. 7 and 8 are partial flow chart block diagrams of the weldingsystem as shown in FIG. 1 combining the preferred embodiment of thepresent invention shown in FIG. 4 with a combined waveform control fromthe embodiments of the invention shown in FIGS. 5 and 6, respectively;

FIG. 9 is a current waveform for the DC positive implementation of thepresent invention;

FIG. 10 is a schematic elevational view showing the invention used inthe root pass or tacking pass of a pipe welding joint;

FIG. 11 is a side elevational view with a block diagram illustrating theuse of a representative welding system and an electrode;

FIG. 12 is an enlarged cross-sectioned pictorial view taken generallyalong line 12-12 of FIG. 11, depicting the electrode in greater detail;

FIG. 13 is an enlarged, schematic view representing a cored electrodewhere the sheath and core are melted at different rates;

FIG. 14 is a view similar to FIG. 13 illustrating the disadvantage of afailure to employ a tailored waveform for welding with cored electrodes;

FIG. 15 is a view similar to FIGS. 13 and 14; and

FIG. 16 is a partial, side elevational view illustrating a coredelectrode in accordance with the present invention and showing the arclength, which length is minimized by use of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION Novel Power Source/Method

In the electric arc welding industry, short arc welding is a commonpractice and involves the four stages I, II, III and IV as schematicallydisclosed in FIG. 2. The power source for performing short arc weldingcan be a transformer based power source; however, in accordance with thepreferred embodiment of the present invention, system A, shown in FIG.1, utilizes a high switching speed inverter based power source B havingan AC supply across lines 10, 14, or a three phase supply, directed toinverter 14 creating a first DC signal across lines 14 a, 14 b. Inaccordance with standard architecture, boost or buck converter 20 isused in power source B for correcting the input power factor by creatinga controlled second DC signal across output lines 22, 24. High switchingspeed inverter 30 converts the second DC signal across lines 22, 24 to awaveform created by a large number of current pulses across output leads32, 34. In accordance with the preferred embodiment of the presentinvention, the waveform across leads 32, 34 is either DC positive or AC;therefore, inverter 30 has an output stage, not shown, that dictates thepolarity of the profiled waveform across leads 32, 34. These leads areconnected to electrode E and workpiece WP, respectively. In accordancewith standard short arc technology, electrode E is an advancing end ofwire W supplied through contact tip 42 from supply spool or drum 40.Thus, wire W is driven toward workpiece WP at a given WFS as acontrolled waveform having the desired polarity is created across thegap between electrode E and workpiece WP. Wire W is preferably a fluxcored wire schematically illustrated in FIG. 1A and shown to include anouter low carbon steel sheath 50 surrounding an internal flux core 52having a fluxing agent and normally including alloying particles. Shunt60 drives feedback current device 62 so the voltage signal on line 64 isrepresentative of the instantaneous arc current of the welding process.In a like manner, device 70 creates a signal on output line 72representative of the instantaneous voltage of the welding process.Controller C of inverter 30 is a digital device, such as a DSP ormicroprocessor, that performs functions schematically illustrated ingenerally analog architecture. As a central component of controller C awaveform generator 100 processes a specific waveform from a state tablestored in memory unit 102 and selected according to the desired weldingprocess by device or circuit 104. Upon selecting the desired short arcwelding process a select signal 104 a is directed to memory unit 102 sothat the state table defining the attributes and parameters of thedesired short arc welding waveform is loaded into waveform generator 100as indicated by line 102 a. Generator 100 outputs the profile of thewaveform at any given time on output line 100 a with the desiredpolarity indicated by the logic on line 100 b. Illustrated power sourceB controlled by digital controller C is of the current control feedbacktype wherein the current representative voltage on line 64 is combinedwith the waveform profile signal on line 100 a by error amplifier 110having an output signal on line 110 a to control pulse width modulator112 in accordance with standard waveform control technology. The outputsignal on line 112 a controls the shape of the waveform across lines 32,34 and the polarity of the particular waveform profile being implementedis set by the logic on line 100 b. In this manner, waveform generator100 controls pulse width modulator 112 to have pulses in line 112 acontrolling the high frequency operation of inverter 30. This inverterswitching frequency is generally greater than 18 kHz and preferablygreater than about 40 kHz. As so far described, power source B withcontroller C operates in accordance with standard technology pioneeredby The Lincoln Electric Company of Cleveland, Ohio. Controller C isdigital, but illustrated in analog format. To implement a short arcwelding process, it is necessary for controller C to receive feedbackinformation regarding a short circuit condition between electrode E andworkpiece WP. This feature of controller C is schematically illustratedas a short circuit detector 120 that creates a logic on line 122 toannounce the existence of a short circuit event SC to waveform generator100. Thus, the generator is informed when there is a short circuit andimplements a waveform in accordance with processing a short circuit asaccomplished in any short arc welding process. As so far described,controller C is standard technology, with the exception of controlling apolarity switch at the output of inverter 30 by the logic on line 100 b.

To practice the invention, controller C is provided with a circuit 150for controlling the melting pulse preparatory to the short circuit.Circuit 150 is digital, but schematically illustrated in analogarchitecture. The functions are implemented by the digital processor ofcontroller C to control the energy of the melting pulse. Such energycontrol circuitry is described in prior copending application Ser. No.11/103,040 filed by applicant on Apr. 11, 2005 (LEEE 200548). This priorapplication is incorporated by reference herein not as prior art, but asrelated technology. As shown in the prior application, the energy of themelting pulse of a pulsed welding waveform can be controlled by circuit150 including multiplier 152 for multiplying the instantaneous signal onlines 64, 72 to provide a signal on line 154 representing theinstantaneous watts of the welding process. The wattage signal or line154 is accumulated by a standard integrator 156 as described in ParksU.S. Pat. No. 4,866,247. Integration of the watt signal on line 154 iscontrolled by waveform generator 100 that creates a pulse start commandshown as block 160 to correspond to the start of the melting pulseindicated by logic on line 162. The starting point is the time t₁ whenthe melting pulse is started by waveform generator 100. Output signal online 164 starts integration of the watt signal on line 154 by integrator156. The integration process is stopped by a logic on line 170 producedby activation of stop pulse device or circuit 172 upon receipt of logicon input line 172 a. Logic on line 172 a toggles device 172 to changethe logic in output lines 172 a and 172 c. The logic on line 172 cinforms the waveform generator that the melting pulse is to stop tochange the profile on output line 100 a. At the same time, the signal online 172 b toggles reset device or circuit 174 to change the logic online 170 to stop integration of the instantaneous watt signal. Thedigital number on output line 156 a is loaded into digital register 180having an output 182 representing the total energy of a given meltingpulse in the short art welding process. This total energy signal iscompared with a desired energy level stored in register 190 to provide adigital number or signal on line 192. Comparator 194 compares the actualenergy for a given pulse represented by a number on line 182 with adesired energy level indicated by the number on line 192. Therelationship between the actual energy and the desired energy controlsthe logic on line 172 a. When the signal from line 182 equals the signalon line 192, comparator 194 changes the logic on line 172 a to stop thepulse as indicated by device or circuit 172. This stops integration andstops the melting pulse being created by waveform generator 100. Circuit150 is employed for performing the preferred embodiment of the presentinvention which changes the reference or desired energy for the meltingpulse by changing the number on line 192 through adjustment of circuit200. The pulse is stopped when the adjusted energy or energy thresholdis reached as determined by the number signal on line 182 as compared tothe signal on line 192. The preferred embodiment of the novel powersource and method used in the combined invention adjusts circuit 200 tochange the reference energy for performing a novel short arc weldingprocess by changing the melting pulse.

Short arc welding system A using power source B with digital controllerC is operated by adjusting circuit 200 to perform the waveform shown inFIG. 3. AC current waveform 200 has a negative melting pulse 212represented by stage I in FIG. 2 where the melting pulse produces moltenmetal 220 on the end of electrode E. The level of current in pulse 212is below current needed for spray arc so there is a transfer by a short.The time t₁ starts the Joule measurement as explained later. The pulsehas a start position 212 a at time t₁ and a stop position 212 b at timet₂. Following the melting pulse, in accordance with standard practice,there is a positive low current quiescent transfer section 214, asrepresented by stage II of FIG. 2. In this stage, the molten metal 220on the end of advancing electrode E is formed into a ball by surfacetension action awaiting a short circuit which occurs at time t₃ and isshown as stage III. Consequently, the time between t₂ and t₃ is the timebetween the end of the melting pulse and the short circuit event, whichtime is indicated by the logic on line 122 as shown in FIG. 1. Afterstage II, a current pinch action shown as neck 222 separates the moltenmetal 220 from puddle 224. This electrical pinching action shown instage IV is accelerated in accordance with standard practice by anegative short circuit pulse 216 having a first current section 216 awith a steep slope and followed by a second current section 216 b with amore gradual slope. Ultimately, the shorted metal separates and the SClogic on line 122 shifts to start the next current pulse at time t₁indicated by a transition section 218. Waveform 210 is an AC waveformhaving a negative melting pulse 212, a low current quiescent section 214and a clearance pulse 216 transitioning into the next negative pulse 212at time t₁. The corresponding voltage has a waveform 230 with negativesection 232, a low level positive section 234 that plunges at short 236and is followed by a negative voltage section 238 that transitions atsection 240 into the next melting pulse voltage 232. The total cycletime is from t₁ to the next t₁ and the positive transfer 214 has a timeless than 20% of the total cycle time. This prevents stubbing.

The present invention involves a novel power source and method forcontrolling waveform 210 by waveform generator 100 of controller C sothe time between the end of melting pulse 212 at t₂ and the time of theactual short event t₃ is constant based upon adjustment of circuit 200.This time delay adjustment, in the preferred embodiment, is accomplishedby the circuit 250 shown in FIG. 4. In this circuit, the time betweenthe melting pulse and at time t₂ and the short circuit at time t₃ is setto a desired level between 0.5 to 2.0 ms. Preferably, the set desiredtime delay is 1.0 ms, which is the level of the signal on line 254.Thus, the numerical number on line 254 is the desired time t₂ to t₃. Theactual time between t₂ and t₃ is determined by timer 260 which isstarted at time t₂ and stopped at time t₃. The timer is reset for thenext measurement by an appropriate time indicated as t₅ which can beadjusted to be located at various positions after t₃, which position isillustrated to be during the melting pulse in FIG. 3. The number on line262 is the actual time between t₂ and t₃. This actual time is stored inregister 270 which is reset at any appropriate time such as time t₂.Thus, the digital data on line 272 is the actual measured time betweent₂ and t₃. This time is compared to the desired time on line 254. Anyerror amplifier can be used to digitally process the relationship ofactual time to the set time. The process is schematically illustrated asa summing junction 280 and digital filter 282 having an output 284 foradjusting circuit 200. The difference between the desired time and theactual time is an error signal in line 284 which increases or decreasesthe desired total energy of circuit 200. The desired total energy isperiodically updated at an appropriate time indicated as t₂ by an updatecircuit 290. Thus, at all times the signal in line 192 of FIG. 1 is thedesired total energy for pulse 212 of the short arc process. This totalenergy is adjusted by any difference between time t₂ and time t₃ so theenergy of pulse 212 maintains a constant or desired time delay for theupcoming short circuit. This time control stabilizes the short arcwelding process of system A.

In FIG. 4, the preferred embodiment of the novel power source isimplemented by changing the energy threshold for the melting pulse tochange the timing between the pulse and the short event. This time canalso be changed by voltage or power of the melting pulse asschematically illustrated in FIGS. 5 and 6. In both of theseembodiments, the time of the melting pulse t₁ to t₂ is maintained fixedas indicated by block 300. During this constant time melting pulse, thevoltage or power is changed to control the time between the pulse andthe short circuit event. In FIG. 5, the number on output line 284 fromfilter 282 controls feedback loop 310 to adjust the voltage of themelting pulse, as indicated by the numerical data on line 312. To adjustthe power for controlling the delay time of the short circuit event, thenumber on output line 284 is used to adjust feedback loop 320, which iscompared to the instantaneous power on line 154 by waveform generator100. The change in power is a numerical value on line 322 which iscompared to the digital number on line 154 for controlling the power ofthe melting pulse. Thus, in the first three embodiments of the presentinvention, the total energy of the waveform, the voltage of the waveformor the power of the waveform is adjusted to maintain a constant timebetween t₂ to t₃ to stabilize the arc and control the short circuitevents of system A shown in FIG. 1.

In accordance with another embodiment of the novel power source, theenergy adjustment of melting pulse 212 is combined with the twomodifications of the present invention illustrated in FIGS. 5 and 6.Such combination controls are shown in FIGS. 7 and 8 wherein priorsumming junction 280 and digital filter 282 are illustrated as combinedin analog error amplifier 330. The component or program has output 332with a logic for stopping the melting pulse when the threshold energyhas been reached, as indicated by the logic on line 182. Thus, the totalenergy of the pulse is controlled together with the pulse voltagecontrol circuit 310 in FIG. 7 and the pulse power control 320 as shownin FIG. 8. Output 312 is combined with output 172 c for controlling thewaveform profile in line 100 a of generator 100. In a like manner, theenergy level is controlled by logic on line 172 c in combination withthe digital information on output line 322 of power pulse controlcircuit 320. Other combinations of parameters can be used to controlmelting pulse 212 to assure an accurate control of the time between themelting pulse and the short circuit event. Such other parameters arewithin the skill of the art in controlling a waveform generator byclosed feedback loops.

The invention is preferably an AC process, as shown in FIG. 4; however,DC positive waveform 400 can be used as shown in FIG. 9. Melting pulse402 has a high positive current 402 a until the pulse is terminated attime t₂. The current, in the DC positive mode, is limited to a levelbelow that needed for spray arc so the metal is not detached withoutshorting. This concept defines the short arc welding process. Then thewaveform transitions into a low level positive current section 404awaiting the short at time t₃. This low level positive current is usedin the preferred embodiment of the present invention and terminates attime t₃. Thereafter, short clearing pulse 410 is created by the waveformgenerator. Pulse 410 has high ramp area 412 and a stepped area 414 tobring the current back up to the high current level 402 a. Variousillustrated embodiments of the present invention can be used inimplementing the positive current waveform 400; however, the logic online 100 b for controlling the polarity of the output waveform on lines32, 34 is not necessary.

Novel Flux Cored Electrode

The preferred implementation of the inventive power source is in pipewelding operation using a novel flux cored electrode as schematicallyrepresented in FIG. 1A. Such pipe welding operation is schematicallyillustrated in FIG. 10 wherein pipe sections 420, 422 define an openroot 424. The present invention as shown in FIG. 4 controls the waveformon wire W as it moves through contact tip 42 to open root 424 of thepipe joint. FIG. 10 shows a particular embodiment using the presentinvention for welding the root pass of a pipe joint to tack the pipesections together for subsequent joining with standard weldingtechniques.

In certain embodiments, the power sources and/or welding operationsaccording to the present invention exhibit one or more of the followingaspects. The current density is generally less than that required forspray welding since the primary mode of metal transfer is short circuitwelding. As in many short circuit processes, a pinch current isestablished depending upon the wire diameter, for example for a 5/64inch flux cored wire, a current of 625 amps can be used. Generally, thepositive current tends to set the arc length. If the positive current isallowed to reach the same level as the negative current arc length, evenfor half a millisecond, the positive current arc will reach anon-desirable length. Generally, positive side control current is in therange of from about 50 amps to about 125 amps, and preferably about 75amps. The negative portion of the wave shape can either be a constantpower or voltage with a slope of from about 5 to 15 percent current.Typically, welding can be performed at about 60 hertz, 10 percentpositive. Since the positive current is set at a relatively low level,the portion that the wave shape is positive is typically less than 20percent.

FIGS. 11 and 12 schematically illustrate a waveform technology welderand/or welding system 510, and a cored electrode 530. The welding systemcomprises a welder 510 having a torch 520 for directing an electrode 530toward workpiece W. The welding system 510 includes a three phase inputpower supply L1, L2, and L3, which is rectified through rectifier 550,560, and a power source 540. The power source 540 provides an output,and specifically, an AC waveform as described in U.S. application Ser.No. 11/263,064, filed Oct. 31, 2005 (LEEE 200663), previouslyincorporated by reference. An arc AC is created between the end ofelectrode 530 and workpiece W. The electrode is a cored electrode with asheath 600 and an internal filled core 610. The core includes fluxingredients, such as represented by particles 610 a. The purpose ofthese ingredients 610 a is to (a) shield the molten weld metal fromatmospheric contamination by covering the molten metal with slag, (b)combine chemically with any atmospheric contaminants such that theirnegative impact on the weld quality is minimized and/or (c) generate arcshielding gases. In accordance with standard practice, core 610 alsoincludes alloying ingredients, referred to as particles 610 b, togetherwith other miscellaneous particles 610 c that are combined to providethe fill of core 610. To optimize the welding operation, it has beennecessary to use solid wire with an external shielding gas. However, inorder to produce a weld with specific mechanical and metallurgicalproperties, specific alloys are required, which can be difficult toobtain in the form of a solid wire. Gas shielding is not always afeasible alternative due to access to gas or difficulty to achieveadequate shielding due to windy conditions, accessibility to clean gasmixtures and difficult terrains. It would be advantageous to thereforeuse a self shielding cored electrode, so that the environment does notaffect the welding.

A common problem caused when using cored electrodes without control ofthe welding waveform profile is illustrated in FIG. 13. The weldingprocess melts sheath 600 to provide a portion of molten metal 630 meltedupwardly around the electrode, as indicated by melted upper end 640.Thus, the sheath of the electrode is melted more rapidly than the core.This causes a molten metal material to exist at the output end ofelectrode 530 without protective gas or chemical reaction created bymelting of the internal constituents of core 610. Thus, arc AC melts themetal of electrode 610 in an unprotected atmosphere. The necessaryshielding for the molten metal is formed when the sheath and core aremelted at the same rate. The problem of melting the molten metal morerapidly than the core is further indicated by the pictorialrepresentation of FIG. 14. Molten metal 650 from sheath 600 has alreadyjoined workpiece W before the core 610 has had an opportunity to bemelted. Thus, the core 610 can not provide the necessary shielding forthe welding process. FIGS. 13 and 14 show the reason why AC weldingusing cored electrodes has not been used for off-shore pipeline weldingand other pipeline welding. However, an AC waveform can be utilized tocontrol the heat input when using a cored electrode.

By controlling the precise profile for the AC waveform used in thewelding process, sheath 600 and core 610 can be made to melt atapproximately the same rate. The failure to adequately coordinate themelting of the sheath with the melting of the core is one reason why ashielding gas SG, as shown in FIG. 15 may be used. The advantage ofcontrolling the profile of the AC waveform is that external shieldinggas SG, may be avoided.

Although control of the AC waveform can lead to significant advantages,as previously noted, in order to provide arc stability and appropriatemelting temperatures and rates, the actual control of the AC waveform,is quite complicated. And, even with the use of sophisticated ACwaveforms, contamination of the weld is possible. Contamination of weldsformed by using sophisticated AC waveforms, is still possible, even ifshielding gas is used. Accordingly, in a preferred aspect of the presentinvention, certain electrode compositions are provided that, when usedin conjunction with AC waveforms, can form strong, tough, and durablewelds, without significant contamination problems, and without thedegree of control otherwise required for the AC waveforms.

Novel Electrodes

When welding by the novel method or power source with a cored electrode,it is desired to have the sheath and core melt at the same rate. Thisoperation promotes homogeneous mixing of certain core materials with theouter sheath, such that the mixture of molten materials chemicallyresists the effects of atmospheric contamination. Alloying elementsrequired to produce desired weld metal mechanical and metallurgicalcharacteristics are uniformly distributed in the weld metal. Inaddition, the protective benefits derived from slag and/or gas-formingconstituents are optimized. As previously noted, this situation isillustrated in FIG. 15. In contrast, FIG. 14 illustrates a situationwhere the sheath has melted more rapidly than the core. In thisdeleterious situation, molten metal 650 from sheath 500 has alreadyjoined workpiece W before core 610 has had an opportunity to be melted.Metal 650 has not been protected from the effects of atmosphericcontamination to the degree that it would have been if the unmelted coreconstituents had actually been melted. Additionally, alloying elementsneeded to achieve desired mechanical and metallurgical characteristicsmay be missing from molten metal 650.

As previously indicated, an electric welder of the type using waveformtechnology can be used for AC welding using a cored electrode, such aselectrode 700 shown in FIG. 16. Such electrode includes an outer steelsheath 710 surrounding core 720 formed of particulate material,including alloying metals and slag or flux materials. By having internalflux or slag materials, there is no need for external shielding gasduring the welding operation. By including alloying material in core720, the puddle of weld metal 740 on workpiece 730 can be modified tohave exact alloy constituents. This is a substantial advantage andreason for using cored electrodes, instead of solid welding wire wherealloying must be accomplished by the actual constituent of the weldingwire. Adjustment of alloying for the weld metal is quite difficult whenusing solid welding wire. Therefore, it is extremely advantageous inhigh quality welding to employ a cored electrode. Arc AR melts sheath710 and melts constituents or fill in core 720 at a rate which can becontrolled to be essentially the same. Contamination in weld metal 740,such as hydrogen, nitrogen and oxygen can cause porosity problems,cracking and other types of physical defects in the weld metal. Thus, itis a challenge to design the welding process to exclude contaminatesfrom the molten weld metal. It is common to use “killing” agents,typically silicon, aluminum, titanium and/or zirconium which willcombine chemically with potential contaminates to prevent them fromforming porosity or harmful inclusions in the weld metal. Furthermore,“scavengers” may also be added to react with hydrogen containing aspecies in order to remove hydrogen from the weld. In order to depositconsistently sound weld metal 740, it has often been necessary to addsuch killing agents in quantities that are themselves detrimental toproperties of the weld metal, such as ductility and low temperaturetoughness. Thus, it is desirable to reduce the exposure of the moltenmetal in arc AR to prevent contamination of the metal passing fromelectrode 700 to workpiece 730 so the killing agents can be minimized.

The novel electrode compositions when used in AC welding, producedesirable welds that are durable, tough, and which are not susceptibleto problems otherwise associated with the use of conventional electrodecompositions. The electrode compositions of the present invention arepreferably used in conjunction with AC waveforms where the positive andnegative shapes of the AC waveform are modified to reduce the overallarc length LA. In this manner, there is less exposure to the atmosphereand less time during which the metal is molten. A detailed descriptionof the AC waveforms and related welding processes, for which the presentinvention electrode compositions are designed, is set forth in U.S.application Ser. No. 11/263,064, filed Oct. 31, 2005 (LEEE 200663),previously incorporated by reference. Indeed, by reducing the arclength, the temperature of the molten metal can be reduced as it travelsfrom the electrode 700 to weld metal puddle 740. Only by using a welderthat can perform an AC welding process with different shapes for thenegative and positive sections, can AC welding with cored electrodes beused effectively in the field. Parameters of the positive and negativeportions of the alternating waveform can be independently adjusted tocompensate for and optimize the melting of both sheath 710 and cored 720for selected electrode 700.

More specifically, the overall invention involves the combination of anovel electrode and an AC welding wherein the positive and negativesections of the waveform are individually adjusted to accomplish theobjective of a low arc length and reduce contamination. Using thisstrategy, the inventive electrode composition, particularly because itis self-shielding, can provide significant advantages. The electrodesare used without shielding gas and depending upon the particularapplication, can rely on deoxidizing and denitriding agents in the corefor additional protection from atmospheric contamination.

The invention provides a synergistic system of a novel welding methodwith a unique set of alloying and flux components in the core of aFCAW-S electrode. As noted, a cored electrode is a continuously fedtubular metal sheath with a core of powdered flux and/or alloyingingredients. These may include fluxing elements, deoxidizing anddenitriding agents, and alloying materials, as well as elements thatincrease toughness and strength, improve corrosion resistance, andstabilize the arc. Typical core materials may include aluminum, calcium,carbon, chromium, iron, manganese, and other elements and materials.While flux cored electrodes are more widely used, metal-cored productsare useful for adjusting the filler metal composition when welding alloysteels. The powders in metal-cored electrodes generally are metal andalloy powders, rather than compounds, producing only small islands ofslag on the face of the weld. By contrast, flux cored electrodes producean extensive slag cover during welding, which supports and shapes thebead.

The alloy/flux system of the present invention comprises particularamounts of a barium source, particular amounts of a lithium source,lithium oxide, iron oxide, and optional amounts of calcium oxide,silicon oxide, and manganese oxide. One or more fluoride, oxide and/orcarbonate salts of barium can be used for the barium source. And, one ormore fluoride and/or carbonate salts of lithium can be used for thelithium source. The alloy/flux system is included in the electrode fill.The electrode fill generally constitutes from about 18 to about 24% ofthe electrode. A preferred alloy/flux system comprises:

-   -   from about 35 to about 55% barium fluoride as the barium source,    -   from about 2 to about 12% lithium fluoride as the lithium        source,    -   from about 0 to about 8% barium carbonate as a secondary barium        source,    -   from about 0 to about 8% lithium carbonate as the secondary        lithium source,    -   from about 0 to about 15% of lithium oxide,    -   from about 0 to about 15% of barium oxide,    -   from about 5 to about 20% of iron oxide,    -   from about 0 to about 5% of calcium oxide,    -   from about 0 to about 5% of silicon oxide,    -   from about 0 to about 5% of manganese oxide, and    -   up to about 25% of aluminum, magnesium, titanium, zirconium, or        combinations thereof, for deoxidation and denitriding and the        remaining metallics optionally including iron, nickel,        manganese, silicon, or combinations thereof. All percentages        expressed herein are percentages by weight unless noted        otherwise. Preferably, the electrode fill composition comprises        from about 35 to about 55% barium fluoride, from about 2 to        about 12% lithium fluoride, from about 0 to about 15% lithium        oxide, from about 0 to about 15% barium oxide, from about 5 to        about 20% iron oxide, and up to about 25% of a deoxidizing and        denitriding agent as previously noted. In other embodiments, the        previously noted preferred electrode fill composition can also        include from about 0 to about 8% barium carbonate. In yet        another embodiment, the preferred electrode fill composition may        additionally include from about 0 to about 8% lithium carbonate.        In yet another embodiment, the preferred fill composition can        include from about 0 to about 5% calcium oxide. In yet a further        embodiment, the electrode fill composition can include from        about 0 to about 5% silicon oxide. And, in another embodiment,        the preferred electrode fill composition can comprise from about        0 to about 5% manganese oxide. Other embodiments include the use        of one or more of these agents, i.e. the barium carbonate,        lithium carbonate, calcium oxide, silicon oxide, manganese        oxide, and combinations thereof.

The preferred embodiment of the novel method comprises applying a firstnegative voltage between an electrode and a substrate to cause at leastpartial melting of the electrode near the substrate. The method alsocomprises applying a positive voltage between the electrode and thesubstrate to promote formation of a flowable mass of material from theelectrode. The method further comprises monitoring for occurrence of anelectrical short between the electrode and the substrate through theflowable mass. The method further comprises upon detecting an electricalshort, applying a second negative voltage between the electrode and thesubstrate. And, the method comprises increasing the magnitude of thesecond negative voltage, to thereby clear the electrical short and forma weld on the substrate from the flowable mass. The preferredcomposition of the electrode fill in a flux cored electrode comprisesfrom about 35 to about 55% barium fluoride, from about 2 to about 12%lithium fluoride, from about 0 to about 15% lithium oxide, from about 0to about 15% barium oxide, from about 5 to about 20% iron oxide, and upto about 25% of a deoxidation and denitriding agent selected from thegroup consisting of aluminum, magnesium, titanium, zirconium, andcombinations thereof. In other embodiments, additional agents can beincorporated in the preferred electrode fill. For instance, from about 0to about 8% barium carbonate can be included. Another embodiment of theelectrode fill composition includes from about 0 to about 8% lithiumcarbonate. Yet another embodiment includes from about 0 to about 5%calcium oxide. Another embodiment includes from about 0 to about 5%silicon oxide. And, yet another embodiment includes from about 0 toabout 5% manganese oxide. In yet a further embodiment, one or more ofthese agents can be added or otherwise included in the electrode fillcomposition. For example, the preferred electrode fill can alsocomprise, in addition to the previously noted proportions of bariumfluoride, lithium fluoride, lithium oxide, barium oxide, iron oxide, andone or more particular deoxidation and denitriding agents from about 0to about 8% barium carbonate, from about 0 to about 8% lithiumcarbonate, from about 0 to about 5% calcium oxide, from about 0 to about5% silicon oxide, and from about 0 to about 5% manganese oxide.

The novel flux/alloy system is modified from traditional flux/alloysystems used for FCAW-S electrodes to achieve the short arc length andto weld at low heat inputs that result from the unique waveforms used inthis process. The short arc length and the stable arc is a result of thecombination of the alloy and flux system and the unique characteristicsof the waveform. In essence, both the welding consumable and the processare optimized in tandem to achieve the final weld product requirements.

In certain embodiments, the present invention provides methods offorming weld metals having attractive properties. Generally, thesemethods involve providing a welding wire or electrode having a core withthe previously described composition. Preferably, the welding wire orelectrode is used free of shielding gas, or rather agents that form sucha gas. The methods also include an operation in which the wire orelectrode is moved toward the region of interest, such as a joint formedbetween two sections of pipe. Preferably such movement is made at acontrolled feed speed. The method also includes creating a weldingcurrent to melt the wire or electrode by an arc between the wire and thepipe sections to thereby form a molten metal bead in the joint. Themethod also includes transferring the melted wire to the molten metalbead by a succession of short circuit events. The method is particularlywell suited for application to welding of a joint between two sectionsof pipe formed from a metal having a yield strength of at least about 70ksi and a thickness less than about 0.75 inches. However, it will beappreciated that the present invention can be used in applications onpipes having thicknesses greater than or less than 0.75 inches. Theresulting bead that is formed generally has a tensile strength greaterthan 70 ksi and in certain applications, greater than about 90 ksi. Inparticular aspects, the melting current can be negative. If the meltingcurrent is negative, the metal transferring operation can be performedby a positive current. The metal transferring can however, be performedby a positive current independent of the melting current. Whenperforming the previously described method, it is generally preferredthat the average arc length is less than 0.30 inches, preferably lessthan 0.20 inches, and most preferably less than 0.10 inches. In thepreviously described method, the rate of the short circuit events ispreferably automatically controlled. The rate of short circuit events isgenerally from about 40 to about 100 cycles per second.

In other embodiments, the previously described concepts, i.e. using thepower sources and control techniques in combination with the novelelectrode compositions noted herein, can be utilized to produce a weldmetal having a minimum Charpy V-Notch toughness of 60 J at −20° C.Similarly, the methods can be used to produce a weld metal having aminimum Charpy V-Notch toughness of 40 J at −40° C. And, the methods canbe used to produce a weld metal having a tensile strength exceeding 90ksi. Thus, thin pipe of less than about 0.75 inches can be used with theresultant savings. No shielding gas is needed, so the cost of on sitegas is eliminated.

The present application can be utilized in a wide array of applications.The system, process, and/or compositions described herein areparticularly adapted for use in welding X80 pipe (the designation X80being in accordance with the API 5L:2000 industry specification) withself-shielded flux core wire. However, the present invention can beutilized in conjunction with other pipe grades. The present inventioncan also be utilized in “root pass” or tack welding operations performedon pipes. The present invention can be utilized to melt greater amountsof welding wire with less arc force as compared to currently knownpractices of using a buried short arc for the initial welding pass. Yetanother application for the present invention is in robotic weldingapplications for high speed welding of thin gauge metals.

The present invention has been described with certain embodiments andapplications. These can be combined and interchanged without departingfrom the scope of the invention as defined in the appended claims. Thesystems, methods, electrodes and combinations thereof as defined inthese appended claims are incorporated by reference herein as if part ofthe description of the novel features of the synergistic invention.

Having thus defined the invention, the following is claimed:
 1. Awelding system for performing a short arc welding process between anadvancing wire electrode and a workpiece where said electrode has an endfacing said workpiece, said system comprising: a power source with acontroller for creating a current pulse introducing energy into said endof said electrode to melt said end and a low current quiescent metaltransfer section following the end of said current pulse during whichsaid melted electrode short circuits against said workpiece; a timer formeasuring an actual time between the end of said current pulse and thebeginning of said short circuit; a device for setting a desired timefrom an end of said current pulse to a beginning of said short circuit;a circuit for creating a corrective signal based upon a differencebetween said actual time and said desired time; and a circuit responsiveto said corrective signal for controlling a given parameter of saidcurrent pulse, wherein said advancing wire electrode is a self-shieldedflux cored arc welding (FCAW-S) wire having an alloy/flux system in acore of said welding wire, said alloy/flux system comprising: from about35 to about 55% barium fluoride; from about 2 to about 12% lithiumfluoride; from about 0 to about 15% lithium oxide; from about 0 to about15% of barium oxide; and from about 5 to about 20% iron oxide.
 2. Thewelding system as defined in claim 1, wherein said low current of saidmetal transfer section has a positive polarity.
 3. The welding system asdefined in claim 1, wherein said controller includes a circuit to createa short circuit clearing pulse after said short circuit prior to a nextcurrent pulse.
 4. The welding system as defined in claim 1, wherein saidgiven parameter is total energy of said current pulse.
 5. The weldingsystem as defined in claim 1, wherein said given parameter is aninstantaneous power of said current pulse.
 6. The welding system asdefined in claim 1, wherein said given parameter is an instantaneousvoltage of said current pulse.
 7. The welding system as defined in claim1, wherein said desired time is in the general range of 0.5-2.0 ms. 8.The welding system as defined in claim 1, wherein said current pulse hasa negative polarity.
 9. The welding system as defined in claim 1, thealloy/flux system further comprising up to about 25% of at least onedeoxidation and denitriding agent selected from the group consisting ofaluminum, magnesium, titanium, zirconium, and combinations thereof. 10.The welding system as defined in claim 1, wherein the alloy/flux systemfurther comprising from about 0 to about 8% barium carbonate.
 11. Thewelding system as defined in claim 1, wherein the alloy/flux systemfurther comprising from about 0 to about 8% lithium carbonate.
 12. Thewelding system as defined in claim 1, wherein the alloy/flux systemfurther comprising from about 0 to about 5% calcium oxide.
 13. Thewelding system as defined in claim 1, wherein the alloy/flux systemfurther comprising from about 0 to about 5% silicon oxide.
 14. Thewelding system as defined in claim 1, wherein the alloy/flux systemfurther comprising from about 0 to about 5% manganese oxide.
 15. Thewelding system as defined in claim 1, wherein the core constitutes fromabout 18 to about 24% by weight of the electrode.
 16. The welding systemas defined in claim 2, wherein said controller includes a circuit tocreate a short circuit clearing pulse after said short circuit prior toa next current pulse.
 17. The welding system as defined in claim 7,wherein said desired time is about 1.0 ms.
 18. The welding system asdefined in claim 9, wherein the alloy/flux system further comprises:from about 0 to about 8% barium carbonate; from about 0 to about 8%lithium carbonate; from about 0 to about 5% calcium oxide; from about 0to about 5% silicon oxide; and from about 0 to about 5% manganese oxide.19. The welding system as defined in claim 16, wherein said clearingpulse has a first current followed by a higher second current.
 20. Thewelding system as defined in claim 19, wherein at least one of saidfirst and second currents is a ramped up current.
 21. A welding systemfor performing a short arc welding process between an advancing wireelectrode and a workpiece wherein said electrode has an end facing saidworkpiece, said system comprising a power source, a timer, a timingdevice, a corrective circuit, a pulse circuit, and said wire electrode;said power source including a controller that creates a current pulsethat introduces energy into said end of said electrode to melt said endand a low current quiescent metal transfer section following an end ofsaid current pulse during which said melted electrode short circuitsagainst said workpiece; said timer measuring an actual time between theend of said current pulse and the beginning of said short circuit; saidtiming device setting a desired time from the end of said current pulseto the beginning of said short circuit; said corrective circuit creatinga corrective signal based upon a difference between said actual time andsaid desired time; said pulse circuit responsive to said correctivesignal to control a given parameter of said current pulse; and said wireelectrode including an alloy/flux system, said alloy/flux systemincluding barium fluoride, lithium fluoride and iron oxide.
 22. Thewelding system as defined in claim 21, wherein said wire electrode is aself-shielded flux cored electrode, said alloy/flux system positioned ina core of said welding wire, said alloy/flux system comprising 35-55weight percent barium fluoride, 2-12 weight percent lithium fluoride, upto 15 weight percent lithium oxide, up to 15 weight percent bariumoxide, and 5-20 weight percent iron oxide.
 23. The welding system asdefined in claim 21, wherein said controller includes a circuitoperatively coupled to said power source to create a short circuitclearing pulse after said short circuit prior to a next current pulse.24. The welding system as defined in claim 21, wherein said givenparameter includes total energy of said current pulse.
 25. The weldingsystem as defined in claim 21, wherein said given parameter includes aninstantaneous power of said current pulse.
 26. The welding system asdefined in claim 21, wherein said given parameter includes aninstantaneous voltage of said current pulse.
 27. The welding system asdefined in claim 21, wherein said desired time is 0.5-2.0 ms.
 28. Thewelding system as defined in claim 21, wherein said welding process hasa cycle time equal to a time of said positive metal transfer section andsaid current pulse, and said metal transfer section time is less than20% of said cycle time.
 29. The welding system as defined in claim 21,wherein said welding process having a current density that is less thanrequired for spray welding of the wire electrode.
 30. The welding systemas defined in claim 21, wherein said pulse circuit is operativelycoupled to said power source and responsive to said corrective signal tocontrol a given parameter of said current pulse to provide asubstantially constant time between the end said current pulse and thebeginning said short circuit.
 31. The welding system as defined in claim21, wherein said pulse circuit is operatively coupled to said powersource and responsive to said corrective signal to control the energy ofsaid current pulse to provide constant rate of shorting.
 32. The weldingsystem as defined in claim 21, wherein said welding process is performedin a root pass of a circuit open root pipe joint by an alternatingcurrent waveform between said advancing wire and a pipe joint and a pipejoint as said workpiece.
 33. The welding system as defined in claim 21,wherein said wire electrode is a flux cored electrode.
 34. The weldingsystem as defined in claim 21, wherein said current pulse to introduceenergy into said end of said electrode is a negative current pulse andsaid metal transfer section has a current of a positive polarity. 35.The welding system as defined in claim 21, wherein a weld bead formed bysaid welding process having a strength of over 60 ksi.
 36. The weldingsystem as defined in claim 22, wherein said alloy/flux system includesat least one deoxidation and denitriding agent, said at least onedeoxidation and denitriding agent constituting up to 25 weight percentof said alloy/flux system, said at least one deoxidation and denitridingagent selected from the group consisting of aluminum, magnesium,titanium, zirconium, and combinations thereof.
 37. The welding system asdefined in claim 22, wherein said alloy/flux system includes calciumoxide, said calcium oxide constituting up to 5 weight percent of saidalloy/flux system.
 38. The welding system as defined in claim 22,wherein said alloy/flux system includes silicon oxide, said siliconoxide constituting up to 5 weight percent of said alloy/flux system. 39.The welding system as defined in claim 22, wherein said alloy/fluxsystem includes manganese oxide, said manganese oxide constituting up to5 weight percent of said alloy/flux system.
 40. The welding system asdefined in claim 22, wherein said alloy/flux system includes bariumcarbonate or lithium carbonate, said barium carbonate or lithiumcarbonate constituting up to 8 weight percent of said alloy/flux system.41. The welding system as defined in claim 22, wherein said alloy/fluxsystem constitutes from 18-24 weight percent of said wire electrode. 42.The welding system as defined in claim 22, wherein said metal transfersection has a current of a positive polarity.
 43. The welding system asdefined in claim 22, wherein said controller includes a circuitoperatively coupled to said power source to create a short circuitclearing pulse after said short circuit prior to a next current pulse.44. The welding system as defined in claim 27, wherein said desired timeis 1.0 ms.
 45. The welding system as defined in claim 33, wherein aprofile of said welding current is controlled to cause a sheath of saidflux cored electrode and said core of flux cored electrode melt at asame rate.
 46. The welding system as defined in claim 43, wherein saidclearing pulse has a first current followed by a higher second current.47. The welding system as defined in claim 46, wherein at least one ofsaid first and second currents is a ramped up current.
 48. A method ofcontrolling a melting pulse of a short arc welding process where amelting pulse for a wire electrode is followed by a low current transfercycle, said method comprising: (a) measuring an actual time for aduration between the end of said melting pulse and the beginning of ashort circuit during said transfer cycle of molten metal from said wireelectrode to a workpiece, said wire electrode including an alloy/fluxsystem, said alloy/flux system including barium fluoride, lithiumfluoride and iron oxide; (b) setting a desired time for said duration;(c) creating a corrective signal by comparing said actual time and saidset time; and (d) adjusting at least one parameter of said melting pulsebased upon said corrective signal so as to regulate said desired timebetween the end of said melting pulse and the beginning of said shortcircuit, said at least one parameter includes a parameter selected fromthe group consisting of (i) total energy, (ii) instantaneous voltage,(iii) instantaneous power, (iv) a combination of total energy andinstantaneous voltage, and (v) a combination of total energy andinstantaneous power.
 49. The method as defined in claim 48, wherein saidcurrent of said transfer cycle is positive.
 50. The method as defined inclaim 48, further comprising: (e) creating a short circuit clearingpulse after said short circuit prior to a next melting pulse.
 51. Themethod as defined in claim 48, wherein said desired time is in the rangeof 0.5-2.0 ms.
 52. The method as defined in claim 48, wherein saiddesired time is about 1.0 ms.
 53. The method as defined in claim 48,wherein said current pulse has a positive polarity.
 54. The method asdefined in claim 48, wherein said current pulse has a negative polarity.55. The method as defined in claim 50, wherein said clearing pulse has afirst current followed by a higher second current.
 56. The method asdefined in claim 54, wherein said current of said transfer cycle ispositive.
 57. The method as defined in claim 55, wherein at least one ofsaid first and second currents is a ramped up current.